The typical process for pyrometallurgic copper production is based on roasting, smelting in furnaces, and converting for production of blister copper. These steps can be followed by further refining of the blister copper into cathode copper. Roasting is performed to reduce impurities, including sulfur, antimony, arsenic, and lead, in the ore and/or concentrate. The roasted product, calcine, serves as a dried and heated charge for the smelting furnace. Smelting of roasted ore concentrate produces matte, a molten mixture of copper sulfide (Cu2S), iron sulfide (FeS), and some heavy metals. Finally, converting the matte yields a high-grade “blister” copper, with 97.5 to 99.5% copper. Matte from the smelting furnace is charged to converters, where the molten material is oxidized in the presence of air to remove iron and sulfur impurities as converter slag and gaseous sulfur dioxide and to form blister copper. Typically a flux is added and air is blown through the molten mixture to remove residual sulfur. Typically, blister copper is then fire-refined in an anode furnace, cast into “anodes”, and sent to an electrolytic refinery for further impurity elimination.
For converting, the Pierce-Smith and Hoboken converters are the most common processes. Pierce-Smith converters are refractory-lined cylindrical steel shells mounted on trunnions at either end, and rotated about the major axis for charging and pouring. An opening in the center of the converter functions as a mouth through which molten matte, siliceous flux, and scrap copper are charged and gaseous products are vented. Air, or oxygen-rich air, is blown through the molten matte. Iron sulfide is oxidized to form iron oxides (FeOx) and SO2. Blowing and slag skimming continue until an adequate amount of relatively pure Cu2S, called “white metal”, accumulates in the bottom of the converter. A final air blast (“final blow”) oxidizes the copper sulfide to SO2, and blister copper forms, containing 98 to 99% copper. The blister copper is removed from the converter for subsequent refining. The SO2 produced throughout the operation is vented to pollution control devices. In the Mitsubishi process the flux is typically limestone (CaCO3) resulting in a CaO comprising slag. The slag also typically comprises 12 to 18% copper, mostly as Cu2O, which can be recycled into the smelting furnace to optimize Cu yield.
Flash furnace smelting combines the operations of roasting and smelting to produce a high grade copper matte from concentrates and flux. In flash smelting, dried ore concentrates and finely ground fluxes are injected together with oxygen, preheated air, or a mixture of both, into a furnace maintained at approximately 1000° C. There are also a number of processes such as Noranda and Mitsubishi, which replace roasting, smelting and converting. As with the Noranda process reactor, and in contrast to reverberatory and electric furnaces, flash furnaces use the heat generated from partial oxidation of their sulfide charge to provide much or all of the required heat.
Flux utilized in the smelting and/or converting steps renders the converting slag more liquid and thus allows lower possible operating temperatures, however the use of it also results in additional energy consumption.